Low-drag perforating gun scallops and method

ABSTRACT

A perforating gun for making perforations in a well, the perforating gun including a carrier extending along a longitudinal axis X and having a bore; a tube extending along the longitudinal axis X and having a radius smaller than a radius of the carrier so that the tube slides inside the bore of the carrier; a shaped charge placed inside the tube and configured to make a hole through the carrier; and a scallop formed in a body of the carrier, corresponding to a location of the shaped charge along the longitudinal axis X. The scallop has a side surface that makes an angle α with the longitudinal axis X, and the angle α is different from 90 degrees.

BACKGROUND Technical Field

Embodiments of the subject matter disclosed herein generally relate to a system and method for delivering one or more perforating guns to a given location in a wellbore, and more particularly, to minimizing the risk of having the one or more perforating guns being caught on casing couplings, perforations or other restrictions that are present in a wellbore.

Discussion of the Background

During a well completion process, a gun string assembly 100, as shown in FIG. 1, which includes plural perforation guns 110 (only one is shown for simplicity), is positioned in an isolated zone in the wellbore's casing 130. The perforating guns 110 are coupled to each other, either through tandems or subs 112. One or more of the perforating guns 110 are then fired, creating holes 113 through the casing 130 and the cement 132 and into the targeted rock formation 134. These perforating holes allow fluid communication between the formation containing the oil and gas, and the wellbore. The firing of the perforating gun detonates charges 116 that are loaded within the perforation gun. Typically, these are shaped charges that produce an explosive-formed penetrating jet in the chosen direction in which the charge is directed.

The perforating gun 110 includes a conveyance for the shaped charges 116, such as a hollow carrier 118, often in the shape of a tube, charge holder end plates (not shown), shaped charges 116, a detonating cord 120, and the detonator 122. The tube 118 with the shaped charges 116 is placed within a gun carrier 124, which body 124′ is made of metal and is configured to prevent a well fluid 136 to reach the shaped charges 116 and the detonator 122. In general, the shaped energetic charges 116 perforate through scallops 126, which are formed on the outside of the body 124′ of the gun carrier 124 of the perforating gun 110. Typical high shot density perforating guns employ an array of shaped charges spaced at intervals along the length of the perforating gun. Each array typically utilizes three or four shaped charges with each array spaced three to four inches apart.

Standard perforating gun scallop (or spotface) designs are features on an inner and/or outer gun carrier 124's body and they are intended to reduce the wall's thickness that a shape charge 116 must fire through. Typical scallops 126 are machined perpendicular to the carrier 124's wall, as shown in FIG. 2. The term “perpendicular” in this context means that a side 127 of the scallop 126 extends along longitudinal axis Z of the shaped charge 116 (the longitudinal axis Z is also the radial axis of the carrier), which is perpendicular on the longitudinal axis X of the carrier 124 or tube 118. Such machining leaves an elevated edge or ridge 128 along the periphery of the scallop 126, i.e., a feature that creates a potential snag point on the carrier 124 that can catch on the casing 130 and increase friction when deploying or retrieving the perforating gun 110 from the wellbore.

Perforating guns are also prone to get caught on casing couplings, perforations, and other restrictions as the standard spot faces typically has a 90 deg angle side wall to the scallop as shown in FIG. 2. In addition, when the shaped charge is angled for angled perforating, the standard scallop with perpendicular sides results in the perforating jet at least partially hitting the carrier wall outside the scallop, thus disturbing the shape of the jet, which results in a decrease in the perforating gun performance and quality of perforation.

Thus, there is a need for a new system that is capable of reducing the thickness of the carrier's wall without negatively impacting the moving of the perforating guns in and out of the wellbore.

BRIEF SUMMARY OF THE INVENTION

According to an embodiment, there is a perforating gun for making perforations in a well. The perforating gun includes a carrier extending along a longitudinal axis X and having a bore, a tube extending along the longitudinal axis X and having a radius smaller than a radius of the carrier so that the tube slides inside the bore of the carrier, a shaped charge placed inside the tube and configured to make a hole through the carrier, and a scallop formed in a body of the carrier, corresponding to a location of the shaped charge along the longitudinal axis X. The scallop has a side surface that makes an angle α with the longitudinal axis X, and the angle α is different from 90 degrees.

According to another embodiment, there is a carrier of a perforating gun for making perforations in a well. The carrier includes a body extending along a longitudinal axis X and having a bore, and a scallop formed in the body of the carrier, corresponding to a location of a shaped charge of the perforating gun along the longitudinal axis X. The scallop has a side surface that makes an angle α with the longitudinal axis X, and the angle α is different from 90 degrees.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic diagram of a perforating gun placed in a horizontal well;

FIG. 2 shows a traditional scallop made in a wall of the carrier of the perforating gun and having a side surface perpendicular to a longitudinal axis of the carrier;

FIG. 3 illustrates a new scallop made in the wall of the carrier and having a side surface that is not perpendicular to the longitudinal axis of the carrier;

FIG. 4 is a perspective view of the scallop and the carrier;

FIGS. 5A and 5B show cross-sectional views of the scallop and the carrier;

FIGS. 6A and 6B show longitudinal sectional views of the scallop and the carrier;

FIG. 7 shows in more detail the shape of the scallop;

FIG. 8 shows another possible shape of the side surface of the scallop;

FIG. 9 shows an angled shaped charge and the location of the scallop to accommodate the jet generated by the such a charge; and

FIG. 10 is a flow chart of a method for making a scallop having non-perpendicular sides.

DETAILED DESCRIPTION OF THE INVENTION

The following description of the embodiments refers to the accompanying drawings. The same reference numbers in different drawings identify the same or similar elements. The following detailed description does not limit the invention. Instead, the scope of the invention is defined by the appended claims. The following embodiments are discussed, for simplicity, with regard to a scallop with a tapered side of 35 degrees relative to a longitudinal axis of the carrier. However, the embodiments to be discussed next are not limited to such a taper angle, but may be applied with other angles, for example, between 15 and 80 degrees.

Reference throughout the specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with an embodiment is included in at least one embodiment of the subject matter disclosed. Thus, the appearance of the phrases “in one embodiment” or “in an embodiment” in various places throughout the specification is not necessarily referring to the same embodiment. Further, the particular features, structures or characteristics may be combined in any suitable manner in one or more embodiments.

According to an embodiment, a novel perforating gun has one or more scallops formed in the body of the carrier, so that the sides of the scallop are not perpendicular to the surface of the body, but rather make an angle, between 15 and 80 degrees, with the surface of the body. This smooth transition spotface side wall is less likely to get stuck or jammed on or with imperfections in the casing.

More specifically, as shown in FIG. 3, a perforating gun 110 has one or more shaped charges 116 distributed within a tube 118, which is placed inside a carrier 124. An external surface 124A of the body 124′ of the carrier 124 has at least a scallop 310 aligned with a corresponding shaped charge 116. The term “aligned” in this context means that a symmetry or longitudinal axis Z of the shaped charge 116 is coincident with a symmetry axis of the scallop 310. A side wall 312 of the scallop 310 makes an angle α with the external surface 124A (which is parallel to the longitudinal axis X of the carrier 124) of the carrier 124, and this angle is between 15 and 80 degrees. In one embodiment, the selection of the value of the angle α is correlated with the value of the internal diameter D of the carrier 124. For example, it has been found by the inventors that for a diameter D of 7.92 cm, the desired angle α is about 35 degrees.

The shape of the scallop 310 and its side surface 312 are further illustrated in FIG. 4. A transversal cross-section A-A through the scallop is shown in FIGS. 5A and 5B and a longitudinal cross-section B-B through the scallop is shown in FIGS. 6A and 6B. It is noted that a bottom surface 314 of the scallop 310 is located within the body 124′ of the carrier 124, and does not communicate with the bore 125 of the carrier 124. FIG. 7 shows these features at a larger scale for easy visualization. The smooth transition side surface 312 is less likely to get stuck or jammed on or with imperfections in the casing 130. FIG. 7 also shows a bore 131 of the casing 130 and how the carrier 124 is placed inside the bore 131 and the scallop 310 faces the inside wall of the casing 130.

While the scallop 310 may have a perfectly circular shape, in one embodiment, as shown in FIG. 6B, the scallop has a bottom circular circumference 610 and a top non-circular circumference 620, for example, an elliptical shape. In this embodiment, the large diameter LD (see FIG. 7) of the top non-circular circumference 620 extends along the X axis while its small diameter SD extends along the circumference of the carrier 124 (see FIG. 6B). These orientations may be changed as necessary.

In another embodiment, the large diameter LD of the top non-circular circumference 620 is selected to be substantially equal to the opening diameter OP of the top surface of the shaped charge 116, i.e., the opening through which the jet is expelled when the shaped charge is fired (see FIG. 3). The term “substantially” is understood herein to mean 10% or less than the reference length.

In yet another embodiment, as illustrated in FIG. 8, the side surface 312 of the scallop 310 may be configured to be curved (for example, the entire surface is curved), with a first radius R1 of curvature for the region 810 defining the top circumference 620 and a second radius R2 of curvature for the region 820 defining the bottom circumference 610. The first and second radii of curvature are different, with the first radius being smaller than the second radius. In this way, the first region 810 and the second region 820 form the side surface 312 of the scallop 310. The first region 810, by being curved and smooth, ensures that there is no strong engagement with the casing 130 when sliding along the casing.

In one application, it is possible to coat the side surface 312 of the scallop 310 (e.g., only the region 810) with a material 830 that has a smaller friction coefficient with the casing 130 than the wall of the carrier 124, so that there is less friction when the perforating gun 110 advances in a horizontal well. The coating material 310 may be placed, for example, only on the region 810, or both on the wall 124A of the carrier 124 and the region 810. In one application, the coating material 810 is graphite, or copper or brass, or an acrylic material or an equivalent material.

In another embodiment, the shaped charge 116 is placed at a non-zero angle β relative to the radial axis R (which is defined as a radial direction of the tube 118), as shown in FIG. 9. This arrangement of the shaped charge is called herein an angled shaped charge. For this situation, depending on the value of the angle β, the position of the scallop 310 is adjusted relative to the body of the carrier 124 so that a central location 810 of the scallop 310 sits on the longitudinal axis Z of the shaped charge 116. This means that the large diameter LD (see FIG. 7) of the scallop 310 is still substantially equal to the outside diameter OD of the shaped charge. To achieve this relationship, the entire location of the scallop 310 is shifted along the longitudinal axis X of the carrier 124. The scallop 310 for this case may have any or all features of the scallops previously discussed, i.e., the various features of the scallops discussed in the previous embodiments may be combined in any way in this or another embodiment. In one application, it is possible that the a and β angles are substantially equal to each other. While the scallops discussed herein have been provided on the outside wall of the carrier 124, the same type of scallop may be provided on the inside wall of the carrier.

With angled perforating as with Geodynamics' SandIQ system, there is an additional benefit of having the scallop 310, in that the shaped charge is also tilted to a similar angle to correspond to the angled or tapered side wall. This combination results in a target spotface that is easier to hit with the charge jet without damaging the side of the carrier. With the “low drag scallop,” the perforating jet has a larger area to shoot thru without hitting the carrier.

A method for making a carrier 124 having one of the scallops 310 discussed above is now discussed with regard to FIG. 10. The method starts with a step 1000 of providing the body 124′ of the carrier, which extends along the longitudinal axis X and has a bore 125. In step 1002, the scallop 310 is machined to have a side surface 312 and a bottom surface 314. This step may include a substep of making the bottom surface 314 to be circular and a top circumference to be non-circular. The side surface 312 is manufactured to make an angle α with the longitudinal axis, and the angle α is different from 90 degrees. In one application, the angle α is between 15 and 80 degrees. The method may further include making the scallop on an external surface of the carrier. The method may also include an optional step 1004 of selecting a value of the angle α to be correlated with a value of an internal diameter of the carrier.

The scallop has a bottom circular circumference and a top non-circular circumference where the top non-circular circumference is elliptical. In one application, the top non-circular circumference has first and second diameters, with the first diameter being larger than the second diameter. The first diameter may be substantially equal to an outside diameter of the shaped charge. In yet another application, which may be combined with any of the previous application or embodiments, the side surface of the scallop is formed of a first region having a first curvature radius and a second region having a second curvature region. The first curvature radius is smaller than the second curvature radius. In one application, a longitudinal axis Z′ of the shaped charge makes a non-zero angle with a radial axis Z of the carrier, and a central point of the scallop is located along the longitudinal axis Z′.

The disclosed embodiments provide a scallop on the wall of the carrier of a perforating gun and the scallop has a side surface not perpendicular to the surface of the wall, so that a smooth contact surface is formed between the carrier and the casing in which the carrier is placed. It should be understood that this description is not intended to limit the invention. On the contrary, the embodiments are intended to cover alternatives, modifications and equivalents, which are included in the spirit and scope of the invention as defined by the appended claims. Further, in the detailed description of the embodiments, numerous specific details are set forth in order to provide a comprehensive understanding of the claimed invention. However, one skilled in the art would understand that various embodiments may be practiced without such specific details.

Although the features and elements of the present embodiments are described in the embodiments in particular combinations, each feature or element can be used alone without the other features and elements of the embodiments or in various combinations with or without other features and elements disclosed herein.

This written description uses examples of the subject matter disclosed to enable any person skilled in the art to practice the same, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the subject matter is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims. 

What is claimed is:
 1. A perforating gun for making perforations in a well, the perforating gun comprising: a carrier extending along a longitudinal axis X and having a bore; a tube extending along the longitudinal axis X and having a radius smaller than a radius of the carrier so that the tube slides inside the bore of the carrier; a shaped charge placed inside the tube and configured to make a hole through the carrier; and a scallop formed in a body of the carrier, corresponding to a location of the shaped charge along the longitudinal axis X, wherein the scallop has a side surface that makes an angle α with the longitudinal axis X, and the angle α is different from 90 degrees.
 2. The perforating gun of claim 1, wherein the angle α is between 15 and 80 degrees.
 3. The perforating gun of claim 1, wherein the scallop is made on an external surface of the body of the carrier.
 4. The perforating gun of claim 1, wherein a value of the angle α is correlated with a value of an internal diameter of the carrier.
 5. The perforating gun of claim 1, wherein the scallop has a bottom circular circumference and a top non-circular circumference.
 6. The perforating gun of claim 5, wherein the top non-circular circumference is elliptical.
 7. The perforating gun of claim 5, wherein the top non-circular circumference has first and second diameters, with the first diameter being larger than the second diameter.
 8. The perforating gun of claim 7, wherein the first diameter is substantially equal to an outside diameter of the shaped charge.
 9. The perforating gun of claim 1, wherein the side surface of the scallop is formed of a first region having a first curvature radius and a second region having a second curvature region.
 10. The perforating gun of claim 9, wherein the first curvature radius is smaller than the second curvature radius.
 11. The perforating gun of claim 1, wherein a longitudinal axis Z of the shaped charge makes a non-zero angle with a radial axis R of the carrier, and a central point of the scallop is located along the longitudinal axis Z.
 12. A carrier of a perforating gun for making perforations in a well, the carrier comprising: a body extending along a longitudinal axis X and having a bore; and a scallop formed in the body of the carrier, corresponding to a location of a shaped charge of the perforating gun along the longitudinal axis X, wherein the scallop has a side surface that makes an angle α with the longitudinal axis X, and the angle α is different from 90 degrees.
 13. The carrier of claim 12, wherein the angle α is between 15 and 80 degrees.
 14. The carrier of claim 12, wherein the scallop is made on an external surface of the body.
 15. The carrier of claim 12, wherein a value of the angle α is correlated with a value of an internal diameter of the carrier.
 16. The carrier of claim 12, wherein the scallop has a bottom circular circumference and a top non-circular circumference.
 17. The carrier of claim 16, wherein the top non-circular circumference is elliptical having first and second diameters, with the first diameter being larger than the second diameter.
 18. The carrier of claim 17, wherein the first diameter is substantially equal to an outside diameter of the shaped charge.
 19. The carrier of claim 12, wherein the side surface of the scallop is formed of a first region having a first curvature radius and a second region having a second curvature region, and wherein the first curvature radius is smaller than the second curvature radius.
 20. The carrier of claim 12, wherein a longitudinal axis Z of the shaped charge makes a non-zero angle with a radial axis R of the carrier, and a central point of the scallop is located on the longitudinal axis Z. 